Introduction: Data on the cause of death form the cornerstone for analyzing the health situation and disease in countries, and they make a major contribution to building evidence for health policies. Aim: The aim of this study was to determine the extent to which diagnoses from the group - Symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R99), International Classification of Diseases (ICD - Revision X) were used as the main cause of death in Serbia, Croatia, North Macedonia, and Slovenia in the ten-year period, 2007 - 2016. Materials and methods: Methods of descriptive and analytical statistics were used in this research. An analysis of data on the causes of death (R00-R99 ICD - Revision X), by gender, during the ten-year period (2007 - 2016) was performed. Linear regression was also used as an analytical method to analyze the trend. Results: During the ten-year period, in Serbia, the R00-R99 diagnoses were among the five most common groups of diagnoses of death, i.e., in each year they took third place, with a percentage of 4.7%. In the observed period, in the surrounding countries, there was an increase in the death rate in Slovenia, with the highest rate in 2016 (19.9), while in Croatia there was a decrease in the death rate related to the diagnoses from group XVIII ICD - X (R00-R99). In Macedonia, the rate had a linear trend, with a slight decline in 2012 (52.3) and 2013 (58.7). In the observed period, an increase in the death rate of the population of Serbia with an unknown cause of death was observed, with particularly high rates in 2009 and 2016. Comparative analysis has shown that R00-R99 diagnoses are represented more in the mortality statistics of Serbia than in Slovenia and Croatia, and less than in Northern Macedonia. Conclusion: Urgent interventions are needed to improve the quality of mortality statistics and data on the causes of death in the described countries.